Printing bead spacers on flat panel display substrates

ABSTRACT

An apparatus for printing bead spacers on a substrate of an LCD panel includes a head unit for spraying a plurality of bead spacer groups on the substrate, a transfer unit for transferring the head unit, and a supply unit for supplying the bead spacers to the head unit. Each of the bead spacer groups includes a plurality of bead spacers, and the sizes of the respective spacers of at least two of the spacer groups are different from each other. The invention enables a cell gap of a substantially uniform thickness to be created and maintained in the panel, prevents the occurrence of smear failures in the panel, and increases the allowable tolerance in the amount of liquid crystal material needed to fill the panel correctly.

RELATED APPLICATIONS

This application claims priority of Korean Patent Application No.10-2006-0041353, filed May 9, 2006, the entire contents of which areincorporated herein by reference.

BACKGROUND

This invention relates to methods and apparatus for printing beadspacers on the substrates of liquid crystal display (LCD) panels.

LCDs are currently the most widely used type of flat panel display, andtypically comprise a display panel having two substrates on which fieldgenerating electrodes are formed, and between which a layer of liquidcrystal material is sealed. The panel adjusts the transmittance of lightpassing through the liquid crystal layer by rearranging the molecules ofthe liquid crystal layer through the application of selected voltages tothe electrodes.

The upper and lower substrates of an LCD panel are coupled together witha sealant that extends around a peripheral edge of the two substrates,and which seals the liquid crystal material between them, and aplurality of spacers are disposed between the upper and lower substratesto define a space with a closely controlled height, called a “cell gap,”between the two substrates.

The spacers may be comprise spherical “bead”-type spacers or“columnar”-type spacers that are disposed in a fixed pattern between thetwo substrates.

The columnar spacers are preferably formed in regions of the displaypanel through which the passage of light is blocked, for example, at thechannel parts of thin film transistors (TFTs), gate lines, storageelectrode lines, and the like, by coating a photosensitive film on acolor filter array substrate of the panel and then exposing anddeveloping it. The bead spacers, on the other hand, are typically formedby randomly spraying them onto one of the substrates before the twosubstrates are sandwiched together.

However, when bead spacers are simply sprayed randomly onto one of thedisplay substrates, the spacers can act like particles of a foreignsubstance that adversely affect the contrast ratio of the display byallowing light to leak through them. Additionally, it is possible forsome of the bead spacers to move slightly and thereby cause damage to analignment layer of the panel.

On the other hand, the use of columnar-type spacers results in anincrease in the number of manufacturing processes required to make thepanel, thereby increasing panel cost. Additionally, unlike bead spacers,which are made of a plastic having a relatively high elasticity,columnar spacers have a relatively low elasticity, and as a result, theallowable tolerance in the amount of liquid crystal material needed tocorrectly fill the space between two the substrates decreases. As aresult, it is easily possible to produce panels that are imperfectly orexcessively charged with the liquid crystal material. Further, becauseof their low elasticity, when an excessive pressure is applied tocolumnar spacers, the display can easily develop a “smear” fault, inwhich the columnar spacers or the color filters disposed below them arebroken.

BRIEF SUMMARY

In accordance with the exemplary embodiments thereof described herein,the present invention provides methods and apparatus for printingspacers on a substrate of an LCD panel that increase the allowabletolerance in the amount of liquid crystal material needed to correctlyfill the panel and the substantially decrease the incidence of displaypanel smear failures. The invention therefore enables the advantages ofboth bead spacers and columnar spacers to be obtained withoutexperiencing the disadvantages of either.

In one exemplary embodiment thereof, an apparatus for printing beadspacers on an LCD substrate in accordance with the present inventioncomprises a head unit for spraying a plurality of groups of bead spacerson the substrate, a transfer unit for transferring the head unitrelative to the substrate, and a plurality of supply units for supplyingthe bead spacers to the head unit. The bead spacer groups are sprayed onthe substrate together with an adhesive that is curable by heat orultraviolet light.

Each of the spacer groups includes a plurality of bead spacers, and thesize of the spacers in at least one of the groups may be substantiallythe same or different from that of the spacers in at least one of theother groups. The material of the spacers in at least one of the groupsmay be the same as or different from that of the spacers of at least oneof the other groups. The size of the spacers supplied by at least one ofthe supply units may be substantially the same as or different from thesize of the spacers supplied by at least one of the other supply units.

The head unit comprises at least one inkjet head having a plurality ofnozzle groups. Each nozzle group includes a plurality of nozzles, andthe size of the respective nozzles of at least two of the nozzle groupsmay be substantially the same or may be different from each other. Thenozzles of at least two nozzle groups may be disposed alternately witheach other in the inkjet head. The sizes of the respective bead spacerssprayed from the at least two nozzle groups may be substantially thesame as or different from each other.

In one exemplary embodiment, the inkjet head of the apparatus includesfirst and second inkjet heads having first and second nozzle groupsrespectively formed therein, and the size of a nozzle of the firstnozzle group and the size of a nozzle of the second nozzle group aredifferent from each other.

An exemplary embodiment of a method for manufacturing an LCD includesspraying a first bead spacer group through a first nozzle group of ahead unit on a first substrate of the LCD, spraying a second bead spacergroup through a second nozzle group of a head unit on the firstsubstrate, and coupling a second substrate in spaced opposition to thefirst substrate.

The head unit includes one or more inkjet heads. The first nozzle groupmay be formed in one inkjet head, and the second nozzle group may beformed in another inkjet head. Alternatively, the first and secondnozzle groups may both be formed in one inkjet head.

The exemplary method may further include supplying the first and secondbead spacers to the head unit from respective first and second supplyunits. The first and second bead spacer groups may be sprayed on thefirst substrate along with an adhesive, which may be a thermosetting oran ultraviolet hardening adhesive, and accordingly, the method mayfurther include applying heat or ultraviolet light to the firstsubstrate after the first and second bead spacer groups have beensprayed thereon to cure the adhesive.

The first bead spacer group may include a plurality of first beadspacers and the second bead spacer group may include a plurality ofsecond bead spacers, and the respective sizes, materials or both therespective sizes and materials of the first and second bead spacers maybe different from each other. The first and second bead spacer groupsmay be formed on a light blocking member, and such that they do notoverlap each other. The first bead spacer group may be positioned in acentral part of the first substrate, and the second spacer group may bepositioned in a peripheral part of the first substrate.

The density of the first bead spacer group may be ⅙ of the pixel densityof the display panel, the density of the second bead spacer group may be⅙ of the pixel density, and the first and second bead spacer groups maybe spaced apart from each other by a selected distance.

Yet another exemplary embodiment of a bead spacer printing apparatus ofthe present invention includes a head unit for spraying a plurality ofbead spacer groups on a substrate, a transfer unit for transferring thehead unit, and a plurality of supply units for supplying the bead spacergroups to the head unit. Each of the bead spacer groups includes aplurality of bead spacers, and the bead spacers that are included in thegroups are of at least two different kinds. Each of the bead spacergroups may include at least two sizes of bead spacers, or each of thebead spacer groups may include at least one bead spacer made of a firstmaterial and at least one bead spacer made of a second material.

Yet another exemplary embodiment of a method for manufacturing an LCDincludes supplying at least two kinds of bead spacers in a supply unit,spraying the at least two kinds of bead spacers on a first substratethrough a nozzle of a head unit that is connected to a supply unit, andcoupling a second substrate in spaced opposition to the first substrate.

A better understanding of the above and many other features andadvantages of the LCD substrate bead spacer printing methods andapparatus of the present invention may be obtained from a considerationof the detailed description of some exemplary embodiments thereof below,particularly if such consideration is made in conjunction with theappended drawings, wherein like reference numerals are used to identifylike elements illustrated in one or more of the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper side perspective view of an exemplary embodiment ofan apparatus for printing bead spacers on a substrate of an LCD inaccordance with the present invention;

FIGS. 2-4 are bottom plan views of respective exemplary embodiments of ahead unit of the spacer printing apparatus of FIG. 1;

FIG. 5 is a partial cross-sectional view of an LCD substrate, showingbead spacers being sprayed thereon with the apparatus;

FIG. 6 is a partial cross-sectional view of the substrate of FIG. 5,showing the bead spacers sprayed on the substrate being cured by theapplication of ultraviolet light or heat;

FIG. 7 is a partial cross-sectional view of two LCD substrates havinggroups of bead spacers interposed therebetween;

FIG. 8 is a partial top plan view of an LCD panel having bead spacersprinted thereon by an exemplary embodiment of a method in accordancewith the present invention;

FIG. 9 is a partial cross-sectional view of the LCD taken along linesIX-IX of FIG. 8;

FIG. 10 is a partial cross-sectional view of the LCD taken along linesX-X of FIG. 8;

FIG. 11 is a top plan view of a substrate of an LCD on which beadspacers have been printed by another exemplary embodiment of a method inaccordance with the present invention;

FIG. 12 is a bottom plan view of another exemplary embodiment of a headunit of an apparatus for printing bead spacers in accordance with thepresent invention; and,

FIG. 13 is a partial cross-sectional view of two LCD substrates having agroup of bead spacers with different sizes disposed therebetween.

DETAILED DESCRIPTION

FIG. 1 is an upper side perspective view of an exemplary embodiment ofan apparatus for printing bead spacers on a substrate of an LCD inaccordance with the present invention, and FIGS. 2-4 are bottom planviews of respective exemplary embodiments of the inkjet heads 400 of ahead unit 700 of the spacer printing apparatus of FIG. 1. FIG. 5 is apartial cross-sectional view of an LCD substrate 210, showing beadspacers being sprayed on the substrate with the novel apparatus.

As illustrated in FIG. 1, the exemplary bead spacer printing apparatusincludes a head unit 700 for spraying bead spacers 320 on a substrate210 of an LCD, a transfer unit 300 for selectably transferring the headunit 700 relative to the substrate 210, and a supply unit 810 forsupplying the bead spacers 320 to the head unit 700. The head unit 700is disposed at a selected height above a stage 500 on which thesubstrate 210 is mounted. As illustrated in FIGS. 2-4, the head unit 700includes at least one inkjet head 400. A head unit 700 having two inkjetheads is illustrated in FIG. 2, and head units 700 having only oneinkjet head each are illustrated in FIGS. 3 and 4, respectively.

A plurality of nozzles 410 a and 410 b are formed in the bottom of theinkjet heads 400, which have an elongated, or bar-like shape, and thefirst nozzles 410 a have a relative large size d1, and the secondnozzles 410 b have a relatively small size d2. Both the first and secondnozzles 410 a and 410 b are disposed sequentially in elongated groups(i.e., #1, #2, . . . , #n). As used herein, a “nozzle group” means aplurality of nozzles of the same size that are disposed in a straightline, and accordingly, it may be seen that first and second nozzlegroups are formed in the bottom of each inkjet head 400.

As illustrated in the exemplary embodiment of FIG. 2, the inkjet head400 includes first and second inkjet heads 400 a and 400 b, with bothinkjet heads 400 a and 400 b being incorporated in the same head unit700. A plurality of the large sized first nozzles 410 a are formed inthe first inkjet head 400 a, and a plurality of the small sized secondnozzles 410 b are formed in the second inkjet head 400 b.

Alternatively, as illustrated in the embodiment of FIG. 3, the largerfirst nozzles 410 a and the smaller second nozzles 410 b may bealternately disposed in a single line in one inkjet head 400. Againalternatively, as illustrated in FIG. 4, the large first nozzles 410 aand the small second nozzles 410 b may be respectively disposed in twoparallel lines on opposite sides of one inkjet head 400.

The head unit 700 is operative to spray bead spacers 320 on thesubstrate 210 through the nozzles 410 a and 410 b, and the transfer unit300 connected to the head unit 700 is operative to move the head unit700 to selected positions relative to the upper surface of theunderlying substrate 210. As illustrated in FIG. 1, the transfer unit300 includes a support 310 for positioning the head unit 700 at aselected height above the substrate 210, a horizontal transfer part 330for transferring the head unit 700 in the X and Y directions, and alifter 340 for raising and lowering the head unit 700 in a directionorthogonal to the X and Y directions.

In order to print the bead spacers 320 at selected positions on thesubstrate 210 disposed on the stage 500, the bead spacers 320 aresprayed through the large and small nozzles 410 a and 410 b of theinkjet head 400 while the head unit 700 is moved in the X directionusing the transfer unit 300. In a preferred embodiment, the bead spacers320 are sprayed on top of a grid-like light blocking member 220 that isformed on the substrate 210.

In operation, a mixture 322 a of large bead spacers 320 a and anadhesive 321 are sprayed through the large first nozzles 410 a of theinkjet head 400, and a mixture 322 b of small bead spacers 320 b and theadhesive 321 are sprayed through the small second nozzles 410 b of theink-jet head 400. The bead spacers 320 a and 320 b are made of anorganic material having a low di-electric constant, such as an acrylicorganic compound, Teflon, benzocyclobutene (BCB), cytop, orperfluorocyclobutene (PFCB) for forming a polymer. The adhesive 321 maybe cured, or hardened, by the application of heat or ultraviolet light,and functions to attach the bead spacers 320 a and 320 b firmly to thesubstrate 210 at the respective positions at which they were printed.

As illustrated in FIG. 1, the supply unit 810 includes a first supplypart 810 a and a second supply part 810 b . The first supply part 810 acontains the mixture 322 a of large bead spacers 320 a and the adhesive321, and the second supply part 810 b contains the mixture 322 b ofsmall bead spacers 320 b and the adhesive 321. A supply line 820 isprovided between the supply unit 810 and the nozzles 410 a and 410 b toconnect them together. The supply line 820 includes a first supply line820 a for connecting the first supply part 810 a to the first nozzle 410a, and a second supply line 820 b for connecting the second supply part810 b to the second nozzle 410 b. The mixture 322 a in the first supplypart 810 a is supplied to the first nozzle 410 a through the firstsupply line 820 a, and the mixture 322 b in the second supply part 810 bis supplied to the second nozzle 410 b through the second supply line820 b.

An exemplary method for manufacturing an LCD using the exemplary beadspacer printing apparatus above is described in detail below inconnection with FIGS. 5-7. FIG. 5 is a partial cross-sectional view ofan LCD substrate 210, showing groups of bead spacers 320 a and 320 bbeing sprayed thereon with the apparatus, FIG. 6 is a partialcross-sectional view of the substrate 210 of FIG. 5, showing the beadspacers sprayed on the substrate being cured by the application ofultraviolet rays or heat, and FIG. 7 is a partial cross-sectional viewof two LCD substrates 100 and 200 having sprayed-on groups of beadspacers 320 a, 320 b interposed therebetween.

Initially, as illustrated in FIG. 5, the mixture 322 a of the first,large bead spacers 320 a and the adhesive 321 and the mixture 322 b ofthe second, small bead spacers 320 b and the adhesive 321 are sprayed onthe substrate 210 through the first and second nozzles 410 a and 410 bof the inkjet head 400, respectively. At this point in the process,leakage of light from the display panel can be prevented by printing themixtures 322 a and 322 b in regions that correspond to the grid-likelight blocking member 220 of the display panel. It is also preferablethat the first and second spacer mixtures 322 a and 322 b be printedsuch that they do not overlap each other. The two mixtures 322 a and 322b may be sprayed simultaneously, or consecutively, i.e., in alternativeembodiments, the first bead spacers 320 a may be sprayed on thesubstrate 210 first, and the second bead spacers 320 b may be sprayed onthe surface of the substrate 210 after the first are sprayed, or,vice-versa.

Next, as illustrated in FIG. 6, the mixtures 322 a and 322 b that weresprayed on the substrate 210 are hardened and firmly attached to thesubstrate 210 by the application thereto of heat or light (for example,ultraviolet rays), such that only the groups of first and second beadspacers 320 a and 320 b remain.

Then, as illustrated in FIG. 7, a common electrode substrate 200,including the substrate 210 on which the first and second bead spacers320 are attached, is attached in spaced opposition to a thin filmtransistor (TFT) array substrate 100 under pressure. During thisprocess, the large bead spacers 320 a are deformed slightly so as tomaintain the desired spacing, or cell space, between the two substratesof the display panel after the two substrates have been are assembledtogether with the liquid crystal material disposed therebetween. Thesmall bead spacers 320 b serve to prevent the occurrence of smearfailures in the display in which larger spacers are damaged due toexternal pressures exerted by the supports of the display when a userapplies a local pressure to the display during use.

Thus, as will be appreciated by those of skill in the art, the inventionenables the advantages of both bead spacers, namely, a higher elasticityand a simpler process of application, and those of columnar spacers,namely, the elimination of light leakage from the display because of theselected positions on the display at which they are formed, to beobtained, without the disadvantages of either, in a simple, easilycontrolled process that provides stable yields.

An exemplary embodiment of an LCD made with the methods and apparatus ofthe present invention is described below with reference to FIGS. 8-10,wherein FIG. 8 is a partial top plan view of an LCD panel having beadspacers printed thereon by an exemplary embodiment of a method inaccordance with the present invention, FIG. 9 is a partialcross-sectional view of the panel taken along lines IX-IX of FIG. 8, andFIG. 10 is a partial cross-sectional view of the LCD taken along linesX-X of FIG. 8;

As illustrated in FIGS. 8-10, an LCD panel according to an exemplaryembodiment of the present invention includes a thin film transistorarray substrate 100 and a common electrode substrate 200 that aredisposed in spaced opposition with each other, with a layer 3 of aliquid crystal material interposed between the two substrates.

The thin film transistor array substrate 100 includes a plurality ofgate lines 121 and a plurality of storage electrode lines 131 formed onan insulating substrate 110 made of a transparent glass, plastic, or thelike. The gate lines 121 each convey a gate signal, and extend generallyin a horizontal direction. Each gate line 121 includes a plurality ofgate electrodes 124 that protrude in a vertical direction, and a widenedend part 129 for connecting to other layers or to an external drivingcircuit.

The storage electrode lines 131 receive predetermined voltages, such asa common voltage, and extend almost parallel to the gate lines 121. Eachof the storage electrode lines 131 is disposed between two adjacent gatelines 121, and is positioned nearer to a lower one of the two gate lines121. Each storage electrode line 131 includes a storage electrode 137that extends in a vertical direction. A gate insulating layer 140 madeof, e.g., silicon nitride (SiNx), or the like, is formed on the gatelines 121 and the storage electrode lines 131.

A plurality of semiconductor stripes 151, which are made of hydrogenatedamorphous silicon (“a-Si”), polycrystalline silicon, or the like, areformed on the gate insulating layer 140. Each semiconductor stripe 151is extends generally in a vertical direction, and includes a pluralityof extensions 154 that extend toward the gate electrodes 124.

In the upper part of the semiconductor stripes 151, a plurality of ohmiccontact stripes and islands 161 and 165, which are made of a materialsuch as n+ hydrogenated amorphous silicon in which silicide or an n-typeimpurity is doped with a high concentration, are formed. The ohmiccontact stripes 161 have a plurality of extensions 163, and theextensions 163 and the ohmic contact islands 165 are formed inassociated pairs and are positioned on the extensions 154 of thesemiconductor stripes 151.

A plurality of data lines 171 and a plurality of drain electrodes 175are formed on the ohmic contacts 161 and 165 and the gate insulatinglayer 140. Each data line 171 is extends generally in a verticaldirection and is insulated from and intersects the gate lines 121, andfunctions to convey a data voltage. Each data line 171 includes a wideend part 179 for connecting a plurality of source electrodes 173 thatextend toward a drain electrode 175 and is bent in a ‘C’ shape tocontact other layers or an external driving circuit. The drain electrode175 is spaced apart from the data line 171 and is positioned at anopposite side of the gate electrode 124. The drain electrode 175includes one widened end part 177 and one bar-shaped end part. Thewidened end part 177 is overlapped with the storage electrode 137 and apart of the bar-shaped end part is surrounded with the source electrode173.

The gate electrodes 124, the source electrodes 173, the drain electrodes175, and an extension 154 of the semiconductor stripes 151 constitute aplurality thin film transistors (TFTs), and a channel of the TFTs isformed in the extension 154 between the source electrode 173 and thedrain electrode 175.

A passivation layer 180 is formed on the data line 171, the drainelectrode 175, and the exposed portion 154 of the semiconductor stripe151. The passivation layer 180 is made of an inorganic insulator, anorganic insulator, or so on, and may have a flat surface. Thepassivation layer 180 has a contact hole 182 for exposing the widenedend part 179 of the data line 171, and a contact hole 185 for exposing apart of the drain electrode 175. A plurality of contact holes 181 forexposing the end parts 129 of the gate lines 121 are formed in thepassivation layer 180 and the gate insulating layer 140.

A plurality of pixel electrodes 190 and a plurality of contactassistants 81 and 82 are formed on the passivation layer 180. These maybe made of a transparent conductive material, such as ITO or IZO, or ofa reflective metal, such as aluminum, silver, chromium, or their alloys.

The pixel electrodes 191 are physically and electrically connected tothe drain electrodes 175 through the contact holes 185 and receive adata voltage from the drain electrodes 175. A pixel electrode 191 towhich the data voltage is applied and a common electrode 270 of a commonelectrode display panel 200 that receives a common voltage generate anelectric field, thereby determining the orientation of the molecules ofthe liquid crystal layer 3 disposed between the two electrodes. Thepolarization of light passing through the liquid crystal layer 3changes, depending on the orientation of liquid crystal molecules.Because the pixel electrode 191 and the common electrode 270 constitutea capacitor (referred to herein as a “liquid crystal capacitor”), theymaintain an applied voltage even after the TFT is turned off.

The pixel electrode 191 and the drain electrode 175 connected theretoare overlapped with the storage electrodes 133 a and 133 b and thestorage electrode line 131. A capacitor, which comprises the pixelelectrode 191 and the drain electrode 175 electrically connected theretoare overlapped with the storage electrode line 131, is referred to as astorage capacitor, and functions to enhance the voltage storagecapability of the liquid crystal capacitors.

The contact assistants 81 and 82 are connected to an end part 129 of thegate line 121 and an end part 179 of the data line 171 through thecontact holes 181 and 182, respectively. The contact assistants 81 and82 supplement the adhesion between the end part 129 of the gate line 121and the end part 179 of the data line 171 and an external apparatus, andalso serve to protect them. A lower alignment layer 11 for aligning themolecules of the liquid crystal layer 3 is formed on the pixelelectrodes 190 and the passivation layer 180.

As illustrated in FIG. 10, the upper, common electrode substrate 210,which is made of transparent glass, plastic, or the like, is positionedabove the lower alignment layer 11 and spaced apart from it by aselected distance. A light blocking member 220 for blocking lightleakage between the pixel electrodes 190 is formed in a grid, or matrixshape on the upper substrate 210.

The light blocking member 220 is disposed opposite to the pixelelectrodes 190, and has a plurality of openings which have substantiallythe same shape as respective ones of the pixel electrodes 190. The lightblocking member 220 also includes opaque, or light-blocking partscorresponding to the gate lines 121, the data lines 171 and the TFTs.

A plurality of red, green, and blue color filters 230R, 230G, and 230Bare also formed on the substrate 210. Most of the color filters 230R,230G, and 230B exist within a region that is surrounded with the lightblocking member 220, and may extend in a vertical direction along a lineof the pixel electrodes 190. The color filters 230R, 230G, and 230B mayalternatively be adapted to display colors other than red, green orblue.

An overcoat 250 is formed on the light blocking member 220 and the colorfilters 230R, 230G, and 230B. The overcoat 250 may be made of an organicinsulator, prevents the color filters 230 from being exposed, andprovides a flat surface. In some alternative embodiments, the overcoat250 may be omitted.

The common electrode 270, which is made of a transparent conductor, suchas ITO and IZO, is formed on the overcoat 250. An upper alignment layer12 is formed on the common electrode 270. Both the lower alignment layer11 and the upper alignment layer 12 may be a horizontal alignment layeror a vertical alignment layer.

As illustrated in FIG. 8, a plurality of large bead spacers 320 c and aplurality of small bead spacers 320 d are printed on the upper alignmentlayer 12. The bead spacers 320 c and 320 d are preferably printed in aregion corresponding to the light blocking member 220. In the exemplaryembodiment illustrated, 6 to 8 bead spacers disposed in a generallycircular shape constitute one group of the spacers, and are disposed inregions corresponding to the TFTs of the thin film transistor arraysubstrate 100. Alternatively, the respective bead spacers 320 c and 320d of the bead spacer groups may be substantially equal in size.

As used herein, a “bead spacer group” means a plurality of bead spacers320 c that are disposed in a single group. The number of bead spacersthat may be included in a bead spacer group can be varied. For example,a group can consist of only one bead spacer, or alternatively, a singlegroup can include 4 to 8 bead spacers. Additionally, the density of thebead spacers 320 c can be varied, but in general, are formed at ⅙ of thepixel density. By “density” is meant the number of bead spacers 320 cthat are formed in a single group on the substrate, and “⅙ of the pixeldensity” means that a group of bead spacers is formed at every sixthpixel electrode 190. Thus, a plurality of large bead spacers 320 c maybe formed on a substrate at ⅙ of the pixel density and a plurality ofsmall bead spacers 320 d may also formed on the same substrate at ⅙ ofthe pixel density. As a result, in an LCD of the present invention, thebead spacers may be formed at ⅓ (i.e., ⅙+⅙=⅓) of the pixel density.

The large bead spacers 320 c contact both display panel substrates 100and 200, but the small bead spacers 320 d act to maintain a selectedminimum spacing from the common electrode panel 200. Printing beadspacers of different sizes on the display substrates thus enables theprevention of smear failures in the display and increases the allowabletolerance in the amount of the liquid crystal that must be disposed inthe panel for correct operation.

FIG. 11 is a top plan view of a substrate 300 of an LCD display panel onwhich bead spacers have been printed by another exemplary embodiment ofthe present invention. As illustrated in FIG. 11, small bead spacers 320f are printed at a peripheral part of the substrate 300, and large beadspacers 320 e are disposed at a central part of the substrate. The beadspacers 320 e and 320 f are formed in regions corresponding to the lightblocking member, and are preferably disposed in circular groups of 6 to8 bead spacers each.

In the exemplary embodiment of FIG. 1, the large bead spacers 320 e areformed at ⅙ of the pixel density and the small bead spacers 320 f arealso formed at ⅙ of the pixel density. As a result, the bead spacers 320e and 320 f together are formed at ⅓ of the pixel density of the LCD. Insuch an LCD, because higher pressures exist at the central part of thesubstrate 300 than at a peripheral part thereof, the size of the cellgap at the central part of the substrate 300 tends to decrease relativeto that at the outer part of the substrate. However, since the size ofthe bead spacers 320 e disposed at the central part of the substrate 300are larger than that of the bead spacers 320 f disposed at theperipheral part thereof, the bead spacers 320 e that are disposed in thecentral part are compressed more, thereby functioning to maintain auniform cell gap over the entire substrate 300.

In another scenario, during the process of filling the panel with theliquid crystal material, the liquid crystal material flows out into theperipheral part of the substrate 300, and the peripheral part of thesubstrate 300 may therefore have a cell gap that is larger than that atthe central part of the substrate 300. Accordingly, the differentlysized bead spacers 320 e and 320 f that are distributed within thesubstrate 300 can be disposed differently than that discussed above, andas needed to accommodate this difference in cell gap size. That is, beadspacers 320 e having a large size may be disposed at the peripheral partof the substrate 300 and the bead spacers 320 f having a small size maybe disposed at the central part thereof the substrate 800 to accommodatethis difference in cell gap size. Alternatively, bead spacers having thesame size but made with different material so as to have differentelasticities may be disposed in the respective portions of the displaypanel to accommodate the cell gap difference.

In the exemplary embodiments discussed above, the sizes of therespective bead spacers of the spacer groups were the same, but itshould be understood that it is possible for a nozzle of one inkjet headto spray groups of spacers in which the size and/or material of thespacers in the group are different from each other. FIG. 12 is a bottomplan view of another exemplary embodiment of a head unit of an apparatusfor printing bead spacers in accordance with the present invention. Asillustrated in FIG. 12, only one inkjet head 400 is provided in the headunit 700 of the exemplary apparatus. The inkjet head 400 includes aplurality of nozzles 410 having the same size formed in the bottomthereof. In this embodiment, two or even more types and/or sizes of beadspacers may be contained in the bead spacer groups that are sprayedthrough each of the nozzles 410. For example, bead spacers having two ormore different sizes may be included in each bead spacer group, and beadspacers made of two or more different materials may be included in eachgroup.

FIG. 13 is a partial cross-sectional view of two LCD substrates 100 and200 having a group of bead spacers with different sizes disposedtherebetween. As illustrated in FIG. 13, the large bead spacers 320 amaintain the cell space between two display panels due to theirdeformation when the two substrates are coupled together under pressureafter the liquid crystal material has been applied to one of thesubstrates. As a result of this arrangement, when a user of the panelapplies a localized pressure to the display panel during use, thesmaller sized bead spacers 320 b function to support the two displaypanels, thereby preventing a smear failure of the display in which thelarger bead spacers are over-compressed and potentially damaged by thepressure.

Thus, as discussed above, the invention enables the advantages of bothbead spacers, which have a higher elasticity and are simpler to apply,and those of columnar spacers, namely, the elimination of display lightleakage, to be realized in a panel of an LCD without experiencing thedisadvantages of either, in a simple, easily controlled process thatprovides stable yields.

According to the exemplary embodiments of the methods and apparatus ofthe invention described and illustrated herein, bead spacers having thesame or different sizes and materials are printed in groups at selectedpositions on a substrate of an LCD panel with an inkjet head such thatthe cell gap of the panel is maintained substantially uniform throughoutthe panel, the occurrence of smear failures in the panel are prevented,and the allowable tolerance in the amount of liquid crystal materialneeded to correctly fill the panel is increased.

By now, those of skill in this art will appreciate that manymodifications, substitutions and variations can be made in and to thespacer printing methods and apparatus of the present invention and theiradvantageous application to the manufacture of LCD substrates withoutdeparting from its spirit and scope. In light of this, the scope of thepresent invention should not be limited to that of the particularembodiments illustrated and described herein, as they are only exemplaryin nature, but instead, should be fully commensurate with that of theclaims appended hereafter and their functional equivalents.

1. An apparatus for printing bead spacers on a substrate of an flatpanel display, comprising: a head unit for spraying a plurality ofgroups of bead spacers on the substrate; a transfer unit fortransferring the head unit relative to the substrate; and, a pluralityof supply units for supplying the bead spacers to the head unit, whereineach of the spacer groups includes a plurality of bead spacers, and thesize of the spacers in at least one of the groups is different from thesize of the spacers in at least one of the other groups.
 2. Theapparatus of claim 1, wherein the size of the spacers within any one ofthe groups is substantially the same.
 3. The apparatus of claim 1,wherein the material of the spacers in at least one of the groups isdifferent from the material of the spacers in at least one of the othergroups.
 4. The apparatus of claim 1, wherein the size of the spacerssupplied by at least one of the supply units is different from the sizeof the spacers supplied by at least one of the other supply units. 5.The apparatus of claim 1, wherein the head unit comprises at least oneinkjet head having a plurality of nozzle groups.
 6. The apparatus ofclaim 5, wherein each nozzle group includes a plurality of nozzles, andthe size of the respective nozzles of at least two of the nozzle groupsare different from each other.
 7. The apparatus of claim 6, wherein thesizes of the respective bead spacers sprayed from the at least twonozzle groups are different from each other.
 8. The apparatus of claim5, wherein the inkjet head includes first and second inkjet heads, firstand second nozzle groups are respectively formed in the first and secondinkjet heads, and the size of a nozzle of the first nozzle group and thesize of a nozzle of the second nozzle group are different from eachother.
 9. The apparatus of claim 5, wherein nozzles of a first nozzlegroup and nozzles of a second nozzle group are alternately disposed inthe at least one inkjet head.
 10. The apparatus of claim 1, wherein thebead spacer groups are sprayed on the substrate together with anadhesive that is curable by heat or ultraviolet light.
 11. A method formanufacturing an flat panel display, the method comprising: spraying afirst bead spacer group on a first substrate through a first nozzlegroup of a head unit; spraying a second bead spacer group on the firstsubstrate through a second nozzle group of the head unit; and, couplinga second substrate in spaced opposition to the first substrate.
 12. Themethod of claim 11, wherein the head unit includes one or more inkjetheads.
 13. The method of claim 12, wherein the first nozzle group isformed in one inkjet head of the head unit and the second nozzle groupis formed in another inkjet head of the head unit.
 14. The method ofclaim 12, wherein the first nozzle group and the second nozzle group areformed in one inkjet head.
 15. The method of claim 11, furthercomprising supplying the first and second bead spacers to the head unitfrom respective ones of first and second supply units.
 16. The method ofclaim 11, wherein the first and second bead spacer groups are sprayed onthe first substrate together with an adhesive.
 17. The method of claim16, wherein the adhesive is a thermosetting or an ultraviolet curingadhesive.
 18. The method of claim 17, further comprising applying heator ultraviolet light to the first substrate after spraying the first andsecond bead spacer groups thereon to cure the adhesive.
 19. The methodof claim 11, wherein the first bead spacer group includes a plurality offirst bead spacers and the second bead spacer group includes a pluralityof second bead spacers, and the respective sizes, materials, or both therespective sizes and materials of the first bead spacers and the secondbead spacers are different from each other.
 20. The method of claim 11,wherein the first and second bead spacer groups are sprayed on a lightblocking member and such that they do not overlap each other.
 21. Themethod of claim 20, wherein the first bead spacer group is positioned ina central part of the first substrate and the second spacer group ispositioned in a peripheral part of the first substrate.
 22. The methodof claim 20, wherein the density of the first bead spacer group is about⅙ of a pixel density of the first substrate, the density of the secondbead spacer group is about ⅙ of the pixel density, and the first andsecond bead spacer groups are spaced apart from each other by a selecteddistance.
 23. An apparatus for printing bead spacers on a substrate ofan flat panel display, comprising: a head unit for spraying a pluralityof bead spacer groups on the substrate; a transfer unit for transferringthe head unit; and, a plurality of supply units for supplying the beadspacers to the head unit, wherein each of the bead spacer groupsincludes a plurality of bead spacers and each of the groups includes atleast two different kinds of bead spacers.
 24. The apparatus of claim23, wherein each of the bead spacer groups includes at least two sizesof bead spacers.
 25. The apparatus of claim 23, wherein each of the beadspacer groups includes at least one bead spacer made of a first materialand at least one bead spacer made of a second material.
 26. A method formanufacturing an flat panel display, the method comprising: supplying atleast two kinds of bead spacers from a supply unit; spraying the atleast two kinds of bead spacers on a first substrate of the flat paneldisplay through a nozzle of a head unit that is connected to the supplyunit; and, coupling a second substrate in spaced opposition to the firstsubstrate.